There is a problem of trucks travelling on roads and highways hitting overhead obstructions such as bridges. Sometimes the problem occurs when the truck driver incorrectly assumes that an upcoming bridge is higher than the height of the track. This can stem from: a) the driver not knowing the height of the truck; b) the driver not knowing the height of the bridge; and/or c) the posted height of the bridge is out-of-date.
In the first two cases, there is an element of driver error. But in the third case, the reason a bridge height might be out-of-date is that over time, the road may be repaved and the distance between the road and the under surface of the bridge changed, or other factors, such as the bridge settling over time. Or, there may be snow or mud on the pavement, or the air temperature may make the pavement expand or contract, or other factors that change the clearance height between the pavement and the bridge. In this case, there may be a posted clearance height, and the driver may know that the height of the truck is less than the posted clearance. But if the posted clearance is wrong —if, for example, the posted clearance is greater than the actual clearance—the cause of the crash may be attributable to the inaccurate information as to the bridge height.
Various systems tor preventing truck/bridge collisions have been proposed. U.S. Pat. No. 5,389,912 disclosed a vehicle mounted system for detecting the height of a vehicle using ultrasound waves that are focused in front of the vehicle.
U.S. Pat. No. 3,232,265 disclosed a vehicle mounted height clearance indicator which includes a flexible, antenna-like height indicator which physically contacts an overhead object and provides a relatively direct indication of the height of the object by mechanical means. Although this clearance indicator is useful owing to its functioning without an electrical supply, a drawback of this device is that it will wear over time given its direct physical contact with obstructions.
U.S. Pat. No. 4,284,971 disclosed an overheight vehicle detection and warning system which is installed along a roadway to measure the vehicle height as it passes the system, and illuminates a warning sign telling the driver of the truck to stop if the vehicle height is greater than an approaching bridge. There is no meaning other than the warning sign that communicates the height indication to the driver.
U.S. Pat. No. 4,789,941 is concerned with a system which uses a computerized vehicle classification system that calculates the height of the vehicle in order to classify the vehicle for toll collection or traffic control purposes. This system is inapplicable for determining the absolute heights of vehicles, as this system rejects the height of the vertical exhaust pipe of a truck, for example, as an anomalous reading because it is not concerned with the absolute height of vehicles, but rather with the classification of the vehicle.
U.S. Pat. No. 4,015,232 disclosed a vehicle mounted ultrasonic distance defector far vehicles that tells the driver how close portions of the vehicle are to horizontally spaced objects such as the distance from a wall to truck bumper.
There is a gap in practical technology that can post an accurate bridge clearance in real time.